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                [Usaco2016 Dec]Cities and States                </h1>
                <p>时间限制：10s&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;  空间限制：128MB</p>			</div>
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                                <h3>题目描述</h3><p><div>To keep his cows intellectually stimulated, Farmer John has placed a large map of the USA on the wal</div>
<div>l of his barn. Since the cows spend many hours in the barn staring at this map, they start to notice</div>
<div>&nbsp;several curious patterns. For example, the cities of Flint, MI and Miami, FL share a very special r</div>
<div>elationship: the first two letters of &quot;Flint&quot; give the state code (&quot;FL&quot;) for Miami, and the first tw</div>
<div>o letters of &quot;Miami&quot; give the state code (&quot;MI&quot;) for Flint.Let us say that two cities are a &quot;special&nbsp;</div>
<div>pair&quot; if they satisfy this property and come from different states. The cows are wondering how many&nbsp;</div>
<div>special pairs of cities exist. Please help them solve this amusing geographical puzzle!</div>
<div></div>
<p></p></p><hr/><h3>输入格式</h3><p><div>The first line of input contains N (1&le;N&le;200,000), the number of cities on the map.The next N lines</div>
<div>&nbsp;each contain two strings: the name of a city (a string of at least 2 and at most 10 uppercase lette</div>
<div>rs), and its two-letter state code (a string of 2 uppercase letters). Note that the state code may b</div>
<div>e something like ZQ, which is not an actual USA state. Multiple cities with the same name can exist,</div>
<div>&nbsp;but they will be in different states.</div>
<div>
<div>依次给出N（1&le;N&le;200,000）个城市名及其州的代码（州代码保证仅有两位）。我们说，两个城市是一个&ldquo;特殊对</div>
<div>&rdquo;，如果他们来自不同的州且A城市的州代码是B城市的城市名首两位，B城市的州代码是A城市的城市名首两位。问</div>
<div>：在给定的信息中有多少个&ldquo;特殊对&rdquo;？</div>
</div>
<div></div>
<p></p></p><hr/><h3>输出格式</h3><p><div>Please output the number of special pairs of cities.</div>
<div>
<div></div>
</div>
<p></p></p><hr/><h3>样例输入</h3><pre>6
MIAMI FL
DALLAS TX
FLINT MI
CLEMSON SC
BOSTON MA
ORLANDO FL</pre><hr/><h3>样例输出</h3><pre>1</pre><hr/><h3>提示</h3><p>没有写明提示</p><hr/><h3>题目来源</h3><p>Silver 鸣谢winmt提供译文</p>
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